The Acquired Immune Deficiency Syndrome (AIDS) results from infection with the human immunodeficiency virus (HIV-1). AIDS is characterized by profound and/or neoplasms in the infected individual. In addition to deficiencies in T mononuclear cells from AIDS patients to make interferon- alpha in response to herpes simplex virus type-1 infected fibroblasts has been observed. This deficiency was strongly correlated with the presence of OI in the patients studied and was also predictive of OI in the follow- up period for those not yet meeting the AIDS case definition. The cells responsible for IFN-alpha production were found to be light density HLA-DR positive cells and shared the phenotype of peripheral blood dendritic cells. In the present application, studies will be undertaken to positively identify the IFN-alpha producing cells, determine the interaction of HIV with this population and determine the mechanism of deficient IFN-alpha production in patients with AIDS and OI. Because the DR-positive cells represent only a small fraction of the mononuclear cells, density gradient techniques and sequential depletions with monoclonal antibodies will be utilized for enrichment. Frequency of IFN-producing cells will be monitored by immunoplaque assay and IFN-gene expression in activated cells will be measured by S1 mapping. Immunocytochemical and immuno-gold techniques for electron microscopy using antibodies to IFN will allow for direct detection of morphology of IFN-alpha producing cells. Enriched IFN-alpha producing cells will be used to determine the effect of HIV on these populations. Whether HIV replicates in and/or kills these cells will be determined and the effect of HIV on functional assays will be investigated. Finally, an evaluation of the mechanism of deficiency of IFN-alpha production in AIDS patients will be undertaken. IFN-alpha producing cells from AIDS patients will be evaluated using techniques developed in this application and functional studies involving co-culture to look for possible suppressor cells or factors will be performed. Together, the proposed experiments involving both basic biology and patient studies should provide important information regarding an important mechanism of AIDS pathogenesis.